P1351

Code

GMC P — Powertrain

IC Circuit High Voltage

Brand: GMC

Type: P — Powertrain

Views: UK: 37 EN: 54 RU: 68

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Page language: EN

Causes

Short to battery voltage on the ignition control (IC) wiring
Faulty ignition coil or ignition control module
Poor or corroded connector or pin at coil/module or PCM/ECM
Open or damaged wiring that is picking up voltage or misrouting battery voltage to the IC circuit
Faulty PCM/ECM driver stage
Aftermarket or incorrect replacement ignition component with wrong impedance

Symptoms

Malfunction Indicator Lamp (MIL) illuminated with P1351 stored
Engine misfire or rough idle (may be one cylinder or multiple)
Reduced engine power, poor acceleration
Intermittent or hard starting; possible no-start condition
Degraded fuel economy
Possible engine stalling or hesitation under load

What to check

Retrieve freeze frame and the complete DTC list with a capable scan tool; record RPM, engine load, battery voltage and coolant temp when fault set
Check for related misfire codes (P03xx) and coil-specific P035x codes
Visually inspect ignition coils/module, harness, connectors and PCM connector for heat damage, corrosion, pin push-out or melted insulation
Check battery voltage and charging system (12–14.5 V)
Backprobe coil/module connector and measure voltages while cranking and running (use insulated tools and take high-voltage safety precautions)
Measure resistance and continuity of coil primary and secondary per OEM spec and check for shorts to battery or ground

Signal parameters

Battery/charging system voltage at rest and running: ~12.0–14.5 V
Ignition coil primary driver voltage: ON (driver grounding) ≈ 0 V; OFF ≈ battery voltage (≈12–14 V)
Pulse width varies with engine speed/load — from fractions of a millisecond at idle to several milliseconds at higher loads (consult OEM for exact pulse widths)
Primary coil resistance: low ohm range (consult vehicle-specific OEM spec)
Ground circuit resistance: low (typically

Diagnostic algorithm

Read and record all stored codes and freeze frame data. Note if P1351 is current or historic and any pending misfire codes.
Perform a visual inspection of ignition coils/modules, wiring harness, and connectors (look for melted insulation, chafing, corrosion, loose pins). Repair any obvious damage.
Verify battery and charging system voltage; correct any low voltage condition before further testing.
With a scan tool, monitor coil control status and misfire counters while cranking and running to reproduce the condition.
Backprobe the coil primary control circuit and measure voltage: confirm it switches between ~0 V (on) and battery voltage (off). If the circuit is continuously high, isolate by disconnecting the coil — if voltage still high at harness, suspect wiring or PCM.
Check continuity between coil connector and PCM pin and inspect for shorts to battery or ground. Repair any shorted/open circuits.
Measure coil primary resistance per OEM spec; replace coil if out of spec or internally shorted.
If wiring and coils check good, swap coil with another cylinder (if applicable) to see if the code follows the coil — this helps identify a bad coil vs wiring/PCM.
If the fault follows the harness or persists with a known-good coil, inspect or replace the harness/connector. If the circuit still reports high after harness/coil replacement, suspect PCM driver failure and consider PCM bench testing/replacement per manufacturer procedure.
Clear codes and perform a test drive under the conditions that set the code to verify repair.
Safety note: ignition secondary circuits carry very high voltages — avoid contact and use proper insulated tools and equipment.

Likely causes

Shorted IC harness conductor to battery or constant 12V (pin-to-pin short)
Intermittent or high-resistance ground at the coil/module or PCM causing voltage anomalies
Failed ignition coil primary or internal short in the coil windings
Damaged connector — melted pins, bent pins, corrosion increasing resistance and causing unusual voltage readings
PCM output transistor in ignition driver has failed and is stuck open/high

Fault status

⚠️ Status

Ignition control (IC) circuit voltage higher than expected detected (P1351). Check ignition coil/module, wiring, connectors and PCM driver circuitry.

🟡 Repair difficulty: Medium

⏱️ Diagnostic time: 1.0 - 2.5 hours

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P1351 — IC Circuit High Voltage